1. Field of the Invention
This invention relates to a glucose and fructose polymer and the method for preparing it using a Lactococcus lactis strain. The exopolysaccharides are natural glucose and fructose polymers. These polymers can be found in several plants and microorganisms and are useful as emulsifiers, thickener and surfactants in the food and medicaments industries.
2. Description of the State of the Art
Fructosans naturally occur in two general forms differentiated by the type of binding between molecules of fructose:inulin, as found in plants, is formed from a column of fructose molecules bound by beta,2-1 links. Levans, formed as microbial products, have a column of fructose molecules bound by beta,2-6 links. The fructosans from plants are smaller (around 100 residues) whilst microbial levans contain more than 3 million residues (Pontis et al., 1985, Biochemistry of Storage Carbohydrates in Green Plants. In: Dey and Dixon (eds). Ch. 5, p. 205. New York, Academic Press).
Microbial Levans are produced with sucrose-based substrates having a variety of microorganisms: Acetobacters (Loewenberg, et al., 1957. Can. J. Microbiol., Vol. 3, p. 643), Achromobacter sp. (Lindberg, G., 1957. Nature. Vol. 180, p. 1141), Aerobacter aerogenes (Srinivasan, et al., 1958. Science. Vol. 127, p. 143), Phytobacterium vitrosum (Belval, et al., 1947. 1948. Compt. Rend. Vol. 224, p. 847 and Vol. 226, p. 1859), Xanthomonas pruni (Cooper, et al., 1935. Biochem. J. Vol. 29, p. 2267), Bacillus subtilis (Dedonder, R., 1966. Meth. Enzymol. Vol. 8, p. 500 and Tanka, et al., 1979. J. Biochem., Vol. 85, p. 287), Bacillus polymyxa (Hestrin et al., 1943. Biochem. J., Vol. 3, p. 450), Aerobacter levanicum (Hestrin, et al., Ibid.), Streptococcus sp. (Corrigen et al., 1979. Infect. Immun., Vol. 26, p. 387), Pseudomonas sp. (Fuchs, A., 1956. Nature. Vol. 178, p. 92) and Corynebacterium laevaniformans (Dias et al., 1962. Antonie Van Leewenhoeck, Vol. 28, p. 63).
There are some reports of levan being produced at very low levels and having low purity to be used industrially.
Other biological polymers such as xantan and dextran gum have been extensively used in the food industry as stabilisers in emulsions and froth in ice-cream, in salad-dressing, etc. (Sharma, S. C., January 1981. J. Food Tech., p. 59). Extracellular polysaccharides produced by microorganisms offer a variety of uses and potentially low costs.
Small quantities of levan are generally produced by sucrose fermentation using Actinomyces viscosus or Aerobacter levanicum strains.
Bacillus polymixa generally produces hetero-polysaccharides having different forms of polymers. Genetically modified E. coli strains have been used for producing levan (Gay, P. et al., 1983. J. Bacteriol. Vol. 153, p. 1424). Furthermore, other aerobic fermentation methods have also been used for producing levan (Jeanes, et al., U.S. Pat. No. 2,673,828; Gaffor, et al., U.S. Pat. No. 3,879,545; Ayerbe, et al., U.S. Pat. No. 4,399,221). The drawback of such processes is that they produce low product yield and problems related to contamination, thereby industrial processes leading to greater productivity are required.